The present invention relates to the field of detecting and measuring impurities in cylindrically shaped transparent media.
Glass rods with a circular cross section are manufactured on a large scale as preliminary product for e.g. semi-conductor or chemical industry. Glass rods are typically produced from a cast by means of an elongation process. However the quality of the produced glass rods strongly depends on the number of contaminants or impurities that are embedded in the glass. In typical production processes of glass rods, the majority of impurities or contaminants consists of gas bubbles embedded in the bulk of the material.
In order to guarantee a quality standard of the glass product, its purity has to be monitored continuously, i.e. the number of gas bubbles embedded in the glass rod per unit volume has to be measured. Determining the purity of a glass rod allows to sort it into different quality categories. Furthermore the permanent or frequent inspection of the glass rod during production allows corrective action to be taken in order to maintain a required quality or purity standard.
The inspection of glass or media that are transparent for a specific wavelength of electromagnetic radiation is known in the prior art by making use of imaging techniques by means of cameras or photo detectors. Such optical inspection methods are mostly limited to surface inspections, hence the detection of surface defects. Volume defects such as particles or gas bubbles embedded in the bulk of a transparent medium can only be inspected and detected when the medium is sufficiently thin or features a plain surface. Optical inspection means that are known in the prior art do not provide detection and measuring of impurities located in the bulk of a medium having a curved surface. Furthermore the optical inspection of a medium featuring a non-planar surface is problematic due to refraction and reflection at the boundary of the medium. In particular, refraction and internal reflections that may occur for specific angles of incidence of the electromagnetic radiation, do not allow a sufficient inspection of the entire bulk medium.
Therefore, there is a need to provide a method and system for detecting impurities in a cylindrically shaped medium that allows inspection of the entire bulk medium.